The present invention relates to an organic semiconductor laser device which is excitable by application of electric energy.
It is known that some organic dyes such as organic fluorescent dyes emit a light of short wavelength such as a wavelength in the region of 400 to 550 nm when they are excited by stimulating rays. The wavelength of thus emitted light is remarkably shorter than the wavelength of a laser light emitted by the conventionally employed inorganic semiconductor laser device, which generally in the wavelength region of 620 to 800 nm. Accordingly, an organic semiconductor laser employing the organic fluorescent dye is expected to become employable in various technical fields, for instance, for giving a photo information recording and reproducing system of increased data storage density.
An organic dye laser in the form of a solution containing an organic fluorescent dye is known. S. R. Forrest et al., Nature, 389, 362 (1997), R. E. Slusher et al., Appl. Phys. Lett. 72, 2230 (1997), and S. R. Forrest et al., Appl. Phys. Lett. 72, 144 (1998) describe an organic semiconductor laser device of light-exciting type which employs a thin laser-emitting material layer arranged on a glass and a planer waveguide as an optical resonator.
However, organic semiconductor lasers of light-exciting type are not favorably employed for incorporation into electric devices for industrial and personal uses
As a light-emitting device which utilizes an organic dye and emits a light by excitation by not light but electric energy, an organic electroluminescence (EL) element is known. The organic electroluminescence element is composed of a positive electrode layer, an electron hole-transporting layer, a light-emitting layer containing an organic dye, an electron-transporting layer, and a negative electrode layer in order, and emits a light on the sides of the electrode layers by applying an electric voltage between both electrode layers. The electroluminescence element, however, has almost no emission directivity. Therefore, the known electroluminescence element cannot be utilized as a laser device.
Accordingly, it is an object of the invention to provide an organic semiconductor laser device which can be excited by electric energy and efficiently emits a laser light.
There is provided by the present invention an organic semiconductor laser device comprising a positive electrode layer, an electron hole-transporting layer, a light-emitting layer containing an organic dye and having an open end, an electron-transporting layer, and a negative electrode layer in order, under the condition that light emitted in the light-emitting layer by applying a voltage between the positive electrode layer and the negative electrode layer is recovered from the open end of the light-emitting layer, wherein the electron hole-transporting layer and the electron-transporting layer satisfy the following conditions:
1 less than n1/n2 and 1 less than n1/n3 
(preferably, 1.05 less than n1/n2 and 1.05 less than n1/n3, more preferably, 1.1 less than n1/n2 and 1.1 less than n1/n3)
wherein n1 is a refractive index of the light-emitting layer determined at a wavelength of the light emitted in the light-emitting layer, n2 is a refractive index of the electron hole-transporting layer determined at the wavelength of the emitted light, and n3 is a refractive index of the electron-transporting layer determined at the wavelength of the emitted light;       0.16     less than                             n          2                xc3x97                  d          2                xc3x97                                                            (                                                      n                    1                                                        n                    2                                                  )                            2                        -            1                              λ            0.16     less than                             n          3                xc3x97                  d          3                xc3x97                                                            (                                                      n                    1                                                        n                    3                                                  )                            2                        -            1                              λ      
wherein n1, n2 and n3 have the same meanings as defined above, d2 stands for thickness of the electron hole-transporting layer, d3 stands for thickness of the electron transporting layer, and xcex stands for the wavelength of light emitted in the light-emitting layer.
FIG. 1 is a sectional view indicating a structure of an organic semiconductor laser device of the invention.
FIG. 2 graphically shows a relationship on an organic semiconductor laser device having 2.11 for n1 (refractive index of the light-emitting layer determined at 510 nm) and 1.96 for n2 (refractive index of the electron hole-transporting layer determined at 510 nm; hence, n12=n1/n2=1.09) between an incident angle (xcex8) of a light having a wavelength (xcex) of 510 nm and a distance (Z) for decreasing the strength of an evanescent wave to reach 1/e.